1. Field of Invention
The invention relates to a luminaire comprising a set of light sources and a set of optical elements. The luminaire in question is one wherein, in particular, the light sources consist of light-emitting diodes (LEDs).
2. Description of Related Art
Luminaires using light emitting diodes can be used, for example, as a street lighting or to illuminate objects in shop-windows. As LEDs are becoming more and more efficient and powerful, the possibilities of using LEDs for said purposes are continuously increasing, whereby the number of LEDs necessary for the required light output is continually decreasing. It is known to position each LED behind an optical element or lens of its own, so that the light of each LED can be directed at the street or object to be illuminated.
A drawback of such a luminaire resides in that the light distribution of a separate LED with the associated lens often is not uniformly distributed, which is caused by the fact that the LED""s incident light on the lens is not uniformly distributed. Since the total light beam is a sum of these individual, not uniformly distributed light beams, the end result too is an uniformly distributed light beam.
It is an object of the invention to alleviate the above drawbacks and to provide a luminaire with a more uniformly distributed light beam.
To achieve this, the luminaire in accordance with the invention comprises a set of light sources which are predominantly situated in a first plane, and a set of substantially identical optical elements which are predominantly situated in a second plane which is substantially parallel to the first plane, the position of at least one light source with respect to an optical element opposite said light source differing from the position of one of the other light sources with respect to an optical element opposite said other light source. As the position of the individual LEDs with respect to the optical element directing the light thereof is always different, the effect is the same as that obtained when one optical element is illuminated in different places by different LEDs. Therefore, the result is a more uniformly distributed light incidence on the optical elements and hence a more uniformly distributed outgoing light beam. Another advantage of the invention resides in that the number of light sources can be selected independently of the number of optical elements. As a result, the light intensity of the luminaire can be more readily adapted by adding or removing light sources, or by switching them on or off, without the desired light pattern being influenced.
Preferably, the set of light sources and the set of optical elements each form a matrix, which matrices have substantially equal dimensions, while the number of rows and/or columns of two matrices are different. An embodiment wherein the number of rows and/or columns of one matrix exceeds the number of rows and/or columns of the other matrix by one yields a good result in practice. By means of such a matrix arrangement, a luminaire can be obtained which can be readily manufactured.
Preferably, the light sources are collimated light sources. By so directing the light from each LED that parallel beams are obtained, by means of reflection and/or refraction, before it is incident on the set of optical elements, a more accurate light distribution of the outgoing beam can be attained.
Preferably, the optical elements are rectangular, and border on each other over at least a part of their circumference. By virtue thereof, it can be ensured that the entire light beam emitted by the set of LEDs passes the set of optical elements, so that no light is lost.
Preferably, the optical elements are provided, on one or both sides, with facets having different angles of inclination. The angles of inclination are preferably calculated from the illumination pattern with which the object should be illuminated. By virtue thereof, it is possible to bring about a very complex and accurate light distribution to meet the particular requirements of the user. Such optical elements even enable text to be projected.
In a preferred embodiment, the optical elements have a sawtooth structure, the facets being formed by substantially parallel prisms. A prism, viewed in a direction in the plane of the optical element, preferably has curved sides. Such prisms can be readily provided on a lens or a lens matrix by means of metal-removing tools.
The invention also relates to an optical element which is provided, on one or both sides, with facets, which facets have different angles of inclination.
The invention also relates to a method of illuminating an object, wherein a set of light sources are positioned predominantly in a first plane, and a set of substantially identical optical elements are positioned predominantly in a second plane which is substantially parallel to the first plane, at least one light source being arranged with respect to an optical element opposite said light source, in a position which differs from the position of one of the other light sources with respect to an optical element opposite said other light source.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.